The aims of the proposed research are to develop a procedure for the purification of normal human arylsulfatase A and to characterize the properties of the enzyme. The deficiency of arylsulfatase A in the metachromatic leukodystrophies (MLD), a group of genetically transmitted disorders associated with mental retardation, results in cellular accumulation of cerebroside sulfate with consequent loss of neurological function. In vitro experiments suggest that effective enzyme replacement therapy might be developed for MLD patients, however, for clinical application sufficient quantities of purified human enzyme must be available. Protein concentrates from urine will be exploited as a readily obtainable source for normal human enzyme. Standard protein fractionation techniques such as salt and solvent precipitation, gel filtration, ion exchange chromatography, and electrophoresis will be employed. The biochemical parameters such as pH optimum, K sub-m and V sub-max, ion effects, transferase activity, and nature of active sites will be established with the purified enzyme. Special emphasis will be placed on conditions required for the hydrolysis of the physiological substrate, cerebroside sulfate.